1. Field of the Invention
The present invention relates to a microwave plasma processing apparatus which generates plasma by using microwaves passing through a dielectric plate and/or a shower plate and plasma-processes an object which is to be processed, and more particularly, to a ceramic member that forms a dielectric plate and/or a shower plate, and a method for manufacturing the ceramic member.
2. Description of the Related Art
A general microwave plasma processing apparatus includes a process chamber which performs processes such as film-formation, etching, ashing, and the like on an object to be processed, such as a glass substrate, a semiconductor substrate, or the like, by using plasma. A gas is introduced into the process chamber, and the microwave plasma processing apparatus uses a microwave introducing unit in order to supply microwaves to the process chamber, which is partitioned by a dielectric plate. For example, the microwave introducing unit may be a radial line slot antenna (RLSA) (hereinafter, referred to as a slot antenna). The microwaves excite the gas and thus plasma is generated in the process chamber. In the microwave plasma processing apparatus, a holding stage on which an object to be processed, such as a glass substrate, a semiconductor substrate, or the like, is held, is disposed in the process chamber so as to face the dielectric plate.
The dielectric plate constitutes a window which maintains a processing space of the process chamber to be airtight and through which microwaves are supplied into the processing space of the process chamber.
Such a general microwave plasma processing apparatus has a structure having only a dielectric window formed by a dielectric plate or a structure having a shower plate as a part of dielectric window.
A plasma processing apparatus disclosed in Japanese Patent Laid-open Publication No. 2004-265919 (Reference 1) has the former structure in which a dielectric plate is formed in a process chamber so as to face a slot antenna, and thus a processing space where plasma processing occurs is maintained airtight by the dielectric plate. In this plasma processing apparatus, microwaves from the slot antenna are supplied into the processing space via a dielectric window formed by the dielectric plate. In this case, a plasma gas such as argon (Ar) is injected between the dielectric plate and a holding stage, that is, the plasma gas is supplied from the dielectric plate down into the processing space.
Japanese Patent Laid-open Publication No. 2006-310794 (Reference 2) discloses a plasma processing apparatus and method in which a plurality of dielectric plates through which microwaves are transmitted are paved in a tile configuration and a plasma-generation gas such as Ar is supplied from spaces between the dielectric plates into a process chamber. A dielectric plate in Reference 2 includes a plurality of dielectric parts.
The microwave plasma processing apparatus having the latter structure, that is, a structure having a shower plate as a dielectric window, includes a circular slot antenna and a circular shower plate that includes a plurality of holes through which a plasma gas such as Ar passes. The shower plate is formed by a dielectric member. Further, a microwave plasma processing apparatus having two shower plates formed one over another has also been proposed.
A dielectric window used as a dielectric plate, dielectric parts, or a shower plate as described above is typically formed of ceramic, such as alumina ceramic.
Hereinafter, a dielectric member such as a dielectric plate, dielectric parts, or a dielectric window including a shower plate, is referred to as a dielectric window.
It is reported that a general microwave plasma processing apparatus described above can form a better film, for example, a better oxide film, when using krypton (Kr) as a plasma-generation gas than when using Ar as the plasma-generation gas.